I have built 2- 5 volt DC power supplies. One seems just fine the other is running hot and noisy. I check the voltage coming out of both transformers(11.7 & 11.9) and they are within .2 v ac. After rectification 1 is 9.4 v dc, and the other is 13.85. What can be causing that? I am thinking that is why one of the regulators is running hot.
Thanks!
Thanks!
Schematic? What type of PSU? A schematic or enough detail to know exactly what it is, is very useful.
What does noisy mean exactly?
Are these PSU connected to a load? If they are switching PSU, they may need to be connected to a load to regulate properly, or at least have a ballast resistor between output and ground to cause a few dozens of mA current flow.
If they are not switching PSU, your rectified DC is too low for both of them, "probably" but without a schematic we can only assume. The second PSU measuring 13.85VDC, is not too far off an expected value if it is powering a load. The first measuring 9.4V seems to have a problem, perhaps a wiring or soldering fault, shorted capacitor or regulator.
Measure the voltage before and after the regulator. Is it the correct/expected value?
An externally hosted image should be here but it was not working when we last tested it.
Not sure if the post is right as I have not done this before. But this is the first Linear power supply. The second is a variation of the first, in that it is done without the coil.
They both have a load on them at time of checking. Regulators are LT1084's.
An externally hosted image should be here but it was not working when we last tested it.
You haven't told us which one works and which one fails. The one with the coil will behave a bit like a choke input supply, although modified by the small input cap. The one without the coil is a cap input supply so it will have much larger but shorter charging pulses. This could make the transformer heat up, also the regulator as it will have a higher input voltage.
I usually run some low value (0.1uF - 1.0 uF) caps right next to linear regulators. They have a different time constant than the larger value caps and thus help suppress possible oscillations. I'd also try running the pair unloaded for a while to eliminate a possible loading problem.
Doc
ChicagoJTW I looked at both trans and the appear to be wired the same. I am not quite sure what phase means though.
agdr: the voltages are as follows with load 13.78 in 5.64 out; no load 5.64 out 15.48 in. Let me explain the out. I am trying to use a music rail at the end of supply and it uses .5 volts.
DF96: the one that is acting up is the one above, I am just guessing it has to do with extra voltage.
thaumaturge: you know I was wondering if that could play a part, but I just didn't know.
Thank you all! Please let me know if anything I have said above gives cause for comment.
Mark
agdr: the voltages are as follows with load 13.78 in 5.64 out; no load 5.64 out 15.48 in. Let me explain the out. I am trying to use a music rail at the end of supply and it uses .5 volts.
DF96: the one that is acting up is the one above, I am just guessing it has to do with extra voltage.
thaumaturge: you know I was wondering if that could play a part, but I just didn't know.
Thank you all! Please let me know if anything I have said above gives cause for comment.
Mark
^ What current does the load consume? It is normal for linear regulators to get hot shedding heat. That the input voltage is higher is what should be happening when using the right VA capacity transformer, it is probably a sign everything is working as expected.
The one you mentioned last does not appear to have a problem, 13.78V in and 5.64V out seems right. The other one seems to have a problem, it should not droop all the way to 9V rectified with ~ 12VAC transformer, assuming you used the same transformers and the same load (or without a load.
It is too confusing talking about two different PSU. Let's stop talking about one of them completely and decide one at a time if something is wrong.
As someone already mentioned, it is good to put a small ~ 0.1uF capacitor (non-electrolytic) right before the regulator.
The one you mentioned last does not appear to have a problem, 13.78V in and 5.64V out seems right. The other one seems to have a problem, it should not droop all the way to 9V rectified with ~ 12VAC transformer, assuming you used the same transformers and the same load (or without a load.
It is too confusing talking about two different PSU. Let's stop talking about one of them completely and decide one at a time if something is wrong.
As someone already mentioned, it is good to put a small ~ 0.1uF capacitor (non-electrolytic) right before the regulator.
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mjock--
The phasing is basically the polarity between primary and secondary windings. The dots on the transformer diagram should match up. You can get uneven output if the wiring isn't correct. Do have pins 8 and 11 jumpered, and are you taking output from pins 7 (positive) and 12 (negative)?
The phasing is basically the polarity between primary and secondary windings. The dots on the transformer diagram should match up. You can get uneven output if the wiring isn't correct. Do have pins 8 and 11 jumpered, and are you taking output from pins 7 (positive) and 12 (negative)?
Pins 7 & 12 cannot be positive nor negative.
They are the output of a transformer and thus must be AC.
AndrewT--
Thanks, I know that. He has pin 7 leading to the positive rail and pin 12 leading to the negative in his schematic. The question is whether he has jumpered the middle two pins as Hammond's data sheet specifies for series connection, or whether they might have been hooked up some other way.
Thanks, I know that. He has pin 7 leading to the positive rail and pin 12 leading to the negative in his schematic. The question is whether he has jumpered the middle two pins as Hammond's data sheet specifies for series connection, or whether they might have been hooked up some other way.
^ are both power supplies reading this powering the exact same load?
The numbers make it look like the load on the one reading 13.85V is only a mild overload on the transformer (transformer current rating or true current capability below what the load consumes) so it causes higher voltage input to the regulator, so the regulator has to drop more voltage thus it runs hotter. This is normal.
The other PSU reading 9.4V input, would appear to have too much of an overload on the transformer, a higher current transformer should be used instead, UNLESS there is something else wrong with the circuit. What is the current used by the load and what is the current rating of the transformer?
If it is merely a case of an overloaded transformer, it will allow the regulator to stay cooler due to lower voltage drop but for a bad reason, you may end up blowing the thermal fuse on the transformer if it were operated for extended periods or in warm weather, in an enclosure, etc.
The numbers make it look like the load on the one reading 13.85V is only a mild overload on the transformer (transformer current rating or true current capability below what the load consumes) so it causes higher voltage input to the regulator, so the regulator has to drop more voltage thus it runs hotter. This is normal.
The other PSU reading 9.4V input, would appear to have too much of an overload on the transformer, a higher current transformer should be used instead, UNLESS there is something else wrong with the circuit. What is the current used by the load and what is the current rating of the transformer?
If it is merely a case of an overloaded transformer, it will allow the regulator to stay cooler due to lower voltage drop but for a bad reason, you may end up blowing the thermal fuse on the transformer if it were operated for extended periods or in warm weather, in an enclosure, etc.
With 400mA current into the load and 13.78V in and 5.64V out, and 8.14V drop * 0.4A = 3.3W, that will make a regulator run on the warm side. Avid 531202B02500G (assuming you used that part # as listed on the schematic) is rated for 7.5C/W (convection) so that's 25C rise. That is approaching 50C in some room ambient conditions, which will feel pretty warm but not painfully hot.
The mystery is why the other supply is being pulled down to 9VDC after the bridge rectifier you may need to pull parts one at a time then take measurements to figure out what is wrong.
The mystery is why the other supply is being pulled down to 9VDC after the bridge rectifier you may need to pull parts one at a time then take measurements to figure out what is wrong.
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I think the problem is that the one with the 10mH choke is behaving a bit like a choke input PSU, even though the choke seems too small for that. The first capacitor is quite small, 120uF, so will have a high ripple voltage. The reactance of the choke means that you can't generate the large pulse needed to charge the second cap. Have you modelled it with PSUD2?
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